Failed runs end with one fatal line; failure lines are errors

A command that exits 1 because files or albums failed now ends with one
fatal line saying how many failed and where to look, so -q never leaves
a non-zero exit unexplained: backup points to failures.json, backup-metadata
to mlDataError in each file's JSON, and fix-missing-thumbnails to its
Failed files list. The progress callbacks of the backup, the metadata
backup and the thumbnail helpers take a level, so every line that reports
a failure is logged at error. The library's operation names are shown in
plain words. The README says which lines are error and warning, and which
summary lines --json replaces.

Model: opus-5-5

test/cli/backup-undecryptable.test.ts

@@ -371,6 +371,24 @@ describe("quak backup with records it cannot decrypt", () => {
         expect(stderr.text).toContain("  Failed:      2\n");
     });
 
+    // The album is an error line. The last line is fatal and counts the files
+    // and the album, so `-q`, which prints fatal lines only, still says why
+    // the backup exits 1.
+    it("logs the album at error, and ends with one fatal line counting the files and the album", async () => {
+        const ctx = {
+            ...context(brokenAccount()),
+            log: stderrLog(stderr, "error"),
+        };
+        expect(await backupCommand(ctx, backupDir(), {})).toBe(1);
+
+        expect(stderr.text).toMatch(
+            /^FAILED album 2: could not be decrypted: /,
+        );
+        expect(stderr.text.split("\n").at(-2)).toBe(
+            `quak: 2 file(s) and 1 album(s) failed; see ${join(backupDir(), "failures.json")} and the FAILED lines`,
+        );
+    });
+
     it("names each album it cannot decrypt in the --json result", async () => {
         expect(await backup(brokenAccount(), { json: true })).toBe(1);